An ionizer which allows a piezoelectric transformer to generate a high voltage so as to be applied to a needle electrode for generating ions has been known as disclosed in Patent Document 1, Japanese Unexamined Patent Application Publication No. 10-302994. The ionizer is operated using the high voltage generated at a secondary section of the piezoelectric transformer upon application of AC low voltage to a primary section thereof. As disclosed in Patent Document 1, the high voltage generated in the secondary section (output side) is applied to a needle electrode for generating ions.
In the ionizer using the piezoelectric transformer, as the electric field is focused onto a top end of the needle electrode to generate ions, the top end is likely to be locally deteriorated. This may cause metal particles to scatter, and as a result, the neutralizing performance becomes deteriorated in a short period. As the needle electrode has a narrow ion generation region, the resultant ion generation amount is small. The ion generation amount may be increased by raising the voltage. However, the electric field at the top end of the needle electrode becomes so intense that generation of ozone which exhibits strong oxidative power is facilitated.